The present invention relates to implantable cardiac stimulation leads having an anchoring mechanism and, more particularly, to a lead construction employing an isodiametric lead body to facilitate extraction of the lead should the need arise.
Pacing leads using an anchoring mechanism for anchoring a distal tip with respect to the inside wall of the heart are well known and very important to a successful pacing system. Passive fixation pacing or defibrillation leads typically employ tines or fins as a means of fixating its distal end into the endocardium to prevent microdislodgment and thereby maintain relatively stable capture and sensing values. Even though tines composed of silicone rubber or other suitable material fold back on themselves when fed through an introducer at implantation, in a well-known manner, the tines tend to dictate the size of the introducer employed. In satisfying the demand in the industry for pacing and defibrillation leads and catheters with ever smaller French sizes, minimizing the overall size of future lead designs is warranted.
An early anchoring mechanism using tines is disclosed in U.S. Pat. No. 3,902,501 to Citron et al. The tined lead provides a plurality of pliant tines that extend from an area adjacent the distal tip and electrode of the lead, the tines forming an acute angle with the lead body. The tines are effective in engaging the trabeculae found in the ventricle as well as the atrium, to maintain the electrode tip in a secure position after the physician has positioned it for a good pacing threshold.
While the tined lead has been highly successful, it has carried one longstanding drawback, namely the problems associated with the lateral projections of the tines at the time of introduction of the lead and/or in attempting to reposition the lead. Basically, the lateral extension of the tines causes an effective increased diameter of the lead at about the distal tip, i.e., the effective diameter is much greater at the distal tip than it is along the length of the lead, which length has a suitable uniform small outer diameter. The tines can get wedged at the time of introduction, particularly in passing through the valve between the atrium and the ventricle for positioning against the inner wall of the right ventride. Further, once the physician has positioned the distal tip against the heart wall, it may be desirable to change that position, in either acute or chronic situations, to obtain a position which offers improved pacing threshold; or to withdraw the lead entirely. In such a situation, withdrawal of the lined anchor mechanism may be difficult, or even impossible, to do without damage to the trabeculae or to a valve.
The difficulty of introducing a pacing lead with a tined anchoring element was recognized in the above-mentioned Citron at al. patent which showed an embodiment which included a mechanism for holding the tines against the electrode body during insertion, while allowing their release once the tip was positioned in proximity to the heart wall. However, the mechanism disclosed has not been effective in achieving the aim of reducing the tip cross-section while reliably providing for release of the tines after insertion of the lead. Further, this mechanism did not have any capability of transforming the tines into a reduced cross-sectional geometry which would permit easier withdrawal of the anchor when and as desired. What remained necessary at that time, and still remains a need in the art, is a design which provides both for avoiding the lateral extension of the tines or other anchor mechanism during introduction, and also one which can withdraw the tines in such a manner as to provide improved characteristics for withdrawing the lead after it has already been positioned against the heart wall.
Since the introduction and commercial success of the tined lead, there have been a number of efforts in the pacing industry, and disclosed in the patent literature, to provide an anchoring mechanism which would provide improved characteristics for minimizing the above-noted problems at introduction and/or repositioning. A patent disclosing an extensible passive fixation mechanism for a pacing lead is U.S. Pat. No. 4,913,164 to Greene et al. This patent shows a mechanism for moving tine-type elements from a first unextended position to a second extended position, or vice versa. However, the mechanism is complex, and the technique of closing the tine-type elements would tend to ensnare the lead tip in prior-engaged trabeculae, rather than provide easy withdrawal. U.S. Pat. No. 4,957,118 to Erlebacher discloses another form of electrode lead having a tine assembly, wherein the tines can be actively moved back and forth between a retracted position and an extended position. However, the mechanism of this disclosure likewise results in a similar problem for extraction, namely the tine element is brought down over or on top of the engaging trabeculae. Further, when in the closed position, the tine end is free and provides a space between the tube casing and the tine which would snag trabeculae when the physician attempts to withdraw the lead.
In U.S. Pat. No. 5,238,007 to Giele et al., the lead has an anchoring mechanism at its tip end which in its normal state provides for fixation of the tip end to the inner heart wall and is transformable into a second state wherein the fixation mechanism is transformed to lie substantially parallel to the lead axis. In the second state, the fixation mechanism presents a reduced effective outer diameter and a substantially continuous smooth outer surface extending proximally back from the lead tip. The lead comprises a telescoping mechanism which is provided at its distal end for axial movement of a portion of the anchoring mechanism, for changing it from a normal state to a temporarily transformed state.
Despite all of the advances already achieved, as just mentioned, there remains a need in the art for a pacing lead which provides an effective anchoring mechanism when the lead is in position while having the ability to reduce the effect of such anchoring mechanism, when desired, such as during introduction or repositioning of the lead. Stated differently, there is a need for minimizing the effective cross-section of an anchor mechanism whereby the anchor mechanism is transformed to a geometry which as closely as possible merges with the cylindrical lead casing, and which does not obstruct withdrawal of the lead when in the transformed state.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.
An implantable cardiac stimulation lead system for use with an implantable stimulation device includes an elongated lead with a conductor extending between distal and proximal ends. A tubular insulating sheath overlies the conductor and has an outer peripheral surface of revolution defined by a radius originating at the longitudinal axis. A tip electrode at the distal end of the lead is attached to the conductor. A proximal connector is in electrical continuity with the stimulation device and coupled to the tip electrode. The insulating sheath is formed with a passive fixation feature formed into the outer peripheral surface for encouraging tissue ingrowth to facilitate stability of the tip electrode when the lead system is implanted. No portion of the passive fixation feature extends radially from the longitudinal axis by a distance greater than the radius of the tubular insulating sheath.
A primary feature, then, of the present invention is the provision of an implantable cardiac stimulation lead having an anchoring mechanism and a lead construction employing an isodiametric lead body.
Another feature of the present invention is the provision of such a stimulation lead which is of isodiametric design and can be employed with an introducer of reduced French size.
Yet another feature of the present invention is the provision of such a stimulation lead in which the isodiametricity of its design will facilitate extraction should the need arise.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.